Underwater vehicles such as torpedoes have conventionally had open propeller propulsion systems. Such open propeller propulsion systems are, however, subject to a number of disadvantages. High noise generation and cavitation are, of course, some of the disadvantages. Other disadvantages include the possibilities of propeller fouling when the torpedo is operated in areas where there is debris in the water. Still other disadvantages relate to the sometime necessity to trail control wires or hydrophones or the like behind the torpedo as it traverses through the water, which raises possibilities of fouling the control wires or hydrophone arrays in the propeller. The prior art has focused on very elaborate constructions for housing and trailing the hydrophone arrays behind a propeller construction, as well as complex arrangements for routing control cables and the like from a torpedo housing to a towed array of sensors or control wires extending behind a propeller.
It is known to provide some improvement, particularly as far as cavitation and noise, by providing a power source for torpedoes and the like which is a propeller enclosed in a shroud or housing. One prior art patent which shows such a shrouded construction is the Jerger U.S. Pat. No. 3,112,610. While a shrouded propeller solves some of the problems associated with the conventional open propeller propulsion design, it does not obviate them all.
It is also known to provide a torpedo or other underwater vehicle with what is known as a jet pump propulsion. Basically, a motor driven pump is provided inside the torpedo or other underwater vehicle with water being taken in, pressurized, and pumped out near the aft end of the torpedo or other underwater vehicle to form a jet pump propulsion unit for the torpedo or other vehicle. One such jet pump arrangement is shown in Wislicenus U.S. Pat. No. 3,575,127. Wislicenus basically shows a torpedo construction having a jet pump in which the jet pump appears to be mounted at the extreme aft end of the torpedo, with a motor provided which is only diagrammatically shown and described as located in a substantially forward direction from the pump. It appears that the primary purpose of the arrangement in Wislicenus is to introduce substantial amounts of radial and transverse direction components into the water flow through the pump arrangement in order to reduce the flow velocity over the impeller blades and thereby reduce the level of radiated noise.
Many general design considerations have to be kept in mind in connection with design of a torpedo or similar underwater vehicle. For example, the separation between the center of gravity and the center of pressure for the torpedo or other underwater vehicle should be small, such that the travel direction and control over that direction can be achieved with small control surfaces or fins. That is, if the center of gravity moves substantially forward with respect to the center of pressure then the control fins or the control surfaces have to be very large to control the travel direction of the torpedo or other underwater vehicle. A similar design consideration relates to the weight of the propulsion hardware for the torpedo or other underwater vehicle. Propulsion hardware is generally typically heavier than electronics and the like which are carded in a torpedo, and the propulsion hardware is generally carded towards the aft end of the torpedo. This makes the torpedo or other vehicle heavier in back, and if the weight is not carefully controlled and minimized, it can affect the characteristics of the vehicle. For example, if the vehicle is not neutrally buoyant but has an angle of attack with regard to the vector of travel through the water, then drag is induced substantially cutting down on the efficiency of the torpedo or other vehicle. It is therefore quite important to minimize to the extent possible the weight of the propulsion hardware for a torpedo or like underwater vehicle.